1. Field of the Invention
The present invention relates to an image information reading apparatus for reading radiation image information recorded on a double-sided stimulable phosphor sheet which emits light from both sides thereof when exciting light is applied to a recording surface thereof.
2. Description of the Related Art
A system is known for recording radiation image information of a subject such as a human body with a stimulable phosphor, and reproducing the recorded radiation image information on a photosensitive medium such as a photographic film, or displaying the recorded radiation image information on a display device such as a CRT or the like.
When a radiation energy such as X-rays, α-rays, γ-rays, electron beams, ultraviolet radiation, or the like is applied to a certain phosphor, it stores part of the applied radiation energy. When exciting light such as visible light is subsequently applied to the phosphor, the phosphor emits light depending upon the stored radiation energy. Such a phosphor is referred to as a stimulable phosphor. A stimulable phosphor is usually used in the form of a sheet which is referred to as a stimulable phosphor sheet.
The above known system includes an image information reading apparatus which comprises a reading unit for reading image information recorded on a stimulable phosphor sheet, and an erasing assembly for erasing remaining image information from the stimulable phosphor sheet after the recorded image information has been read. In the image information reading apparatus, a cassette housing a stimulable phosphor sheet which bears radiation image information of a subject recorded by an external exposure device is inserted into a loading unit.
Thereafter, the lid of the cassette is opened, and then the stimulable phosphor sheet is taken out of the cassette by a sheet feeding mechanism. The stimulable phosphor sheet is delivered to the reading unit by a sheet delivering mechanism. In the reading unit, the recorded image information is read from the stimulable phosphor sheet, and then the remaining image information is erased from the stimulable phosphor sheet in the erasing assembly, after which the stimulable phosphor sheet is placed into the cassette which has been disposed in the loading unit.
It has been desired to efficiently read the energy that has been stored in the stimulable phosphor sheet as in the field of mammography. To meet such a demand, there has been an attempt to use a transparent base in the stimulable phosphor sheet. When the exciting light is applied to the stimulable phosphor sheet from the side of a phosphor layer (recording surface) thereof, the stimulable phosphor sheet emits light from the base (reverse surface) as well as the phosphor layer. Therefore, the reading unit has two light guiding means disposed respectively on both sides of the stimulable phosphor sheet for guiding the light emitted therefrom.
The reading unit has a structure with roller pairs for gripping and feeding the stimulable phosphor sheet while holding the reverse surface thereof in contact with guide means in order to read the recorded radiation image information highly accurately. The guide means comprises a plurality of separate guide means at the position where the exciting light is applied to the stimulable phosphor sheet, for guiding the emitted light to the guiding means that is disposed on the side of the reverse surface of the stimulable phosphor sheet.
When the stimulable phosphor sheet is transferred from one of the guide means to the other guide means in the vicinity of the position where the exciting light is applied to the stimulable phosphor sheet, the stimulable phosphor sheet is brought into direct contact with the other guide means comprising, for example, a glass guide, possibly resulting in damage caused to the reverse surface of the stimulable phosphor sheet. Another problem is that, when the leading end of the stimulable phosphor sheet abuts against the other guide means, the stimulable phosphor sheet is caused to flutter, and the image read therefrom suffers undesirable irregularities.